During partial load operation of a gas turbine, the combustion temperature in the combustion chamber typically drops. This also causes a drop in the primary zone temperature (TPZ), i.e. also the combustion chamber temperature, which is relevant for CO emissions. If the temperature falls below a predefined minimum value of the TPZ (e.g. TPZ<1400, ° C. for 10 , ppmv CO emissions), the production of CO emissions increases, and as a result the limit of the useful partial load range of the gas turbine—which conforms to CO emissions limits—is reached. Where legal limits on CO emissions exist, this circumstance can force the operator of the gas turbine to switch off the gas turbine since it is sometimes no longer possible to further reduce the power of the gas turbine without simultaneously exceeding the relevant CO emissions limit.
One technical solution, known to the applicant from the internal prior art, for reducing CO emissions in partial load operation relates to diverting and bypassing cooling air so as to reduce the quantity of compressor outlet air which enters the combustion chamber. Thus, combustion in the combustion chamber can take place with a relatively large quantity of fuel and at a relatively high TPZ, thus reducing CO emissions. The pipes required for bypassing and diverting cooling air, or the pipe ends generally designed as outflow and inflow line stubs, are in this case securely attached to the gas turbine casing. When considering these components and their arrangements, it is particularly important to ensure that both the mechanical and the operational stability of the gas turbine is not greatly influenced.
Furthermore, also with regard to attaching the pipes or the pipe ends, it is important to ensure that the accessibility of the gas turbine for maintenance purposes is not markedly restricted. In that regard, attaching such pipes is subject to limits relating to stability, operation and maintenance.